In semiconductor devices that operate on the basis of clock signals, such as digital circuits, semiconductor devices that handle high-frequency signals, such as high-frequency circuits, and the like, the semiconductor devices are mounted on a printed circuit board. In this state, noise produced by current fluctuations can be superposed on a power source line and have a negative effect on the semiconductor device. A bypass capacitor (decoupling capacitor) is provided near a power supply terminal of the semiconductor device to remove such noise.
Meanwhile, a BGA (“Ball Grid Array”) type semiconductor package including an interposer is an example of a packaged semiconductor device mounted on a surface of a printed circuit board (“semiconductor package” hereinafter).
FIG. 13 is a cross-sectional view illustrating several examples of a conventional mounting structure for the stated semiconductor package and the stated bypass capacitor. In each of examples (A), (B), and (C) in FIG. 13, a semiconductor element 2 is mounted on an upper surface of an interposer 1, the semiconductor element 2 is resin-sealed using a sealing resin 4, and bumps 3 are formed on a lower surface of the interposer. In the example (A), the semiconductor element 2 is wire-bonded to the upper surface of the interposer 1, a bypass capacitor 5 is mounted on a printed circuit board 6, and the semiconductor package is mounted thereupon. In the example (B), the semiconductor element 2 is flip-chip mounted onto the upper surface of the interposer 1. In the example (C), the bypass capacitor 5 is mounted on the lower surface of the interposer 1. In other words, the bypass capacitor 5 is mounted on the semiconductor package side.
Patent Document 1 discloses an example in which a bypass capacitor is mounted on a lower surface of a BGA-type semiconductor package.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-150283.
In the conventional mounting structures of the semiconductor package illustrated in FIGS. 13(A)-(C), there is a large distance from the semiconductor element 2 to the bypass capacitor 5 in the mounting structures of the semiconductor package indicated in (A) and (B), and thus an equivalent serial inductance (ESL) is high. However, in the mounting structure of the semiconductor package indicated in (C), the length of a current path from the semiconductor element 2 to the bypass capacitor 5 is short, and thus the ESL is low and a noise reduction effect is high.
However, the BGA-type semiconductor package disclosed in Patent Document 1 has the following problems to be solved.
(a) The interposer included in the BGA-type semiconductor package disclosed in Patent Document 1 is normally a glass epoxy substrate. Meanwhile, the bypass capacitor is a multi-layer ceramic capacitor (MLCC) having what is known as a dog bone-type terminal structure, in which electrodes are formed on five faces on both sides of the capacitor. A glass epoxy substrate and an MLCC have very different coefficients of linear expansion, and there is thus a risk of cracks forming at joint areas thereof depending on the thermal histories thereof.
(b) An MLCC element is ceramic, and therefore hard and brittle. Accordingly, when a BGA-type semiconductor package warps, stress concentrates at the joint areas thereof, which makes it easy for cracks to form in the joint areas.
(c) An MLCC has a dog bone-type terminal structure, and it is thus difficult to reduce gaps between the terminal and adjacent solder balls. There is thus a risk of short-circuits between the MLCC and interconnects on the printed circuit board where the BGA-type semiconductor package is to be mounted. It is also easy for stray capacitance arising between the interconnects of the printed circuit board and the MLCC to increase. In other words, an MLCC is not suited to a package in which solder balls are disposed at a high density.
As such, it is difficult to ensure bonding reliability between a chip capacitor and an interposer of a semiconductor package, and superior electrical characteristics with a small size and high density cannot be achieved.